1. Field
The present application relates to a fuel cell.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell includes a unit cell including a membrane electrode assembly (MEA) and a pair of separators sandwiching the MEA therebetween. The MEA includes an electrolyte membrane made from a polymer ion-exchange membrane, an anode electrode disposed on one side of the electrolyte membrane, and a cathode electrode disposed on the other side of the electrolyte membrane. Typically, a predetermined number of unit cells of this type are stacked and used as a vehicle fuel cell stack.
A fuel cell includes a metal separator that is press-formed so as to have a corrugated form. A fuel gas channel (hereinafter, also referred to as a reactant gas channel) for supplying a fuel gas to the anode electrode or an oxidant gas channel (hereinafter, also referred to as a reactant gas channel) for supplying an oxidant gas to the cathode electrode are formed in a surface of the metal separator. In each power generation cell or in each set of power generation cells, a coolant channel for supplying coolant is formed along the in-plane direction of the metal separator.
In this case, the coolant channel is formed between the back side of the fuel gas channel and the back side of the oxidant gas channel. Accordingly, in a case where a fuel gas channel and an oxidant gas channel are formed on separators each made by forming a thin metal plate so as to have a wave-like pattern, a coolant channel is formed by overlapping the wave-like shapes on the back sides of wave-shaped channels so that the phases of the wave-like shapes differ from each other.
For example, in a fuel cell described in Japanese Unexamined Patent Application Publication No. 2003-338300, at least one of a first hollow protruding portion that forms a fuel gas channel and a second hollow protruding portion that forms an oxidant gas channel is bent so that part of a top surface of the first hollow protruding portion and part of a top surface the second hollow protruding portion are separated from each other and a connection channel are formed between them. Therefore, the fuel cell can be efficiently cooled because cooling water can flow through the connection channel.
In some cases, the wave-shaped channels of the fuel gas channel and the oxidant gas channel extend in a horizontal direction. For example, in order to install a fuel cell in a space having a limited height, it is necessary that the fuel cell have a horizontally elongated shape. Accordingly, it is preferable that the fuel gas channel and the oxidant gas channel be formed so as to make the fuel gas and the oxidant gas flow in the horizontal direction.
Therefore, each of the wave-shaped channels has recessed portions that are curved or bent downward and then extend upward. Accordingly, water tends to accumulate in such recessed portions that are disposed at a lower position in the vertical direction. In such a recessed portion, for example, metal ions may dissolve into water from a separator and a precious metal may dissolve into water from an electrode. Thus, a problem arises in that, when the dissolved ions are trapped in an electrolyte membrane, the electrolyte membrane deteriorates and the performance of the electrodes decreases.
Moreover, in general, at end portions of an electrode, a higher tension and a higher shearing stress are likely to be applied to the electrolyte membrane than at a central portion of the electrode.